Amplitude shift keyed receiver

ABSTRACT

An amplitude shift keyed (ASK) receiver includes a signal receiving part receiving an amplitude shift keyed signal, a signal detecting part coupled to the signal receiving part and detecting a signal having a carrier frequency and a noise, a pulse detecting part coupled to the signal receiving part and checking the signal from the signal receiving part for compensating errors in the signal detecting part, and a signal determining part coupled to the signal detecting part and the pulse detecting part, the signal determining part determining and restoring a signal to be restored according to output signals from the signal detecting part and the pulse detecting part.

This application claims the benefit of Korean Patent Application No.45052/1996 filed Oct. 10, 1996, which is hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an ASK(Amplitude Shift Keyed) receiver,and more particularly, to an ASK receiver using a digital circuit.

2. Discussion of the Related Art

An ASK technique is a modulation technique used in communicationtechnology. For digital signals such as `0` and `1`, one signal iscarried with a frequency and the other is carried without a frequency asshown in FIG. 1. A conventional ASK receiver will be explained withreference to FIG. 2.

As shown in FIG. 2, a conventional ASK receiver includes apre-amplifying part 1 for amplifying an amplitude shift keyed andreceived signal, a band pass filter 2 for passing a signal only within apredetermined band of the signals from the pre-amplifying part 1, adetector 3 for obtaining an original low frequency signal from an outputof the band pass filter 2, a delaying part 4 for delaying a signal fromthe detector 3 for a predetermined period of time, a signal stretcher 5for stretching a signal from the detector 3 using a capacitor, a dynamicthreshold generator 6 for generating a threshold value for determiningwhether the received signal exceeds a noise level, and a microprocessor7.

The operation of the conventional ASK receiver having the aforementionedsystem will now be explained. Referring to FIG. 2, in order to obtain asignal only within a predetermined band, an amplitude shift keyed andreceived signal is amplified through the pre-amplifying part 1 andfiltered by the band pass filter 2. The filtered signal is received atthe detector 3. The detector 3 generates a high bit level pulse if acarrier signal is present and produces a low bit level pulse if nocarrier signal is detected. Then, the output signal from the abovedetector 3 is inputted to the delaying part 4, the signal stretcher 5,and the dynamic threshold generator 6, respectively. The delaying part 4delays the signal generated from the detector 3 for a predeterminedperiod of time, and the signal stretcher 5 stretches the signal using acapacitor. The dynamic threshold generator 6 produces a threshold valuefor determining whether a received signal exceeds a noise level. Thosesignals from the detector 3 delayed for a predetermined period of timeby the delaying part 4 that are greater than the threshold valuegenerated from the threshold generator 6 and at the same time have asection greater than the signal stretched in the signal stretcher 5 areproduced as a high bit digital signal. The signals in the remainingsections are produced as low bit digital signals. Finally, the outputtedvalues are transmitted to the microprocessor 7 and converted to binarydigit signals.

However, the conventional ASK receiver has the following problems.First, the conventional ASK receiver uses an analog signal system whichhas low reliability and high power consumption. Second, realization of ahighly integrated device with other digital circuits is difficult, and aseparate analog power source generates high noise level.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to an amplitude shiftkeyed receiver that substantially obviates one or more of the problemsdue to limitations and disadvantages of the related art.

An object of the present invention is to provide an amplitude shiftkeyed receiver with high reliability and lower power consumption.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be from the description,or may be learned by practice of the invention. The objectives and otheradvantages of the invention will be realized and attained by thestructure particularly pointed out in the written description and claimshereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, theamplitude shift keyed receiver using an infrared ray used thereinincludes a signal receiving part receiving an amplitude shift keyedsignal, a signal detecting part coupled to the signal receiving part anddetecting a signal having a carrier frequency and a noise, a pulsedetecting part coupled to the signal receiving part and checking asignal from the signal receiving part for compensating errors in thesignal detecting part, and a signal determining part coupled to thesignal detecting part and the pulse detecting part and determining andrestoring a signal to be restored according to output signals from thesignal detecting part and the pulse detecting part.

In another aspect of the present invention, the receiver includes apre-amplifying part amplifying a received amplitude shift keyed signalto a predetermined amplitude, a quantizing part coupled to thepre-amplifying part and amplifying a signal from the pre-amplifying partand digitizing the signal, an ASK edge counting part coupled to thequantizing part and determining a presence of carrier frequency in asignal from the quantizing part, an oscillating part coupled to the ASKedge counting part and generating a clock signal at predeterminedintervals and informing the ASK edge counting part to start count edgesof the amplitude shift keyed signal, a comparing part coupled to the ASKedge counting part and comparing an output from the ASK edge countingpart with a predetermined reference value, a pulse detecting partcoupled to the signal receiving part and checking a signal from thesignal receiving part for compensating errors in the oscillating part,the ASK edge counting part, and the comparing part, a counter and randompart coupled to the comparing part and the pulse detecting part andcombining signals from the ASK edge counting part and the pulsedetecting part to restore a signal, and a hexadecimal counting partcoupled to the counter and random part and a clock signal and receivingsignals from the counter and random part and the clock signal andrestoring the signal to original signal.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 illustrates digital signals carried with a frequency and withouta frequency.

FIG. 2 illustrates a system block diagram of a conventional amplitudeshift keyed receiver;

FIG. 3 illustrates a system block diagram of an amplitude shift keyedreceiver in accordance with a preferred embodiment of the presentinvention; and

FIGS. 4A-4F illustrate signal timings in the amplitude shift keyedreceiver of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

FIG. 3 is an example of a device suitable for short distance radiocommunications such as communications between personal computers orpersonal computer to printer.

As shown in FIG. 3, the amplitude shift keyed receiver of the presentinvention includes a signal receiving part 21 for receiving an amplitudeshift keyed (ASK) signal. A signal detecting part 22 detects a signalhaving a carrier frequency (or signal having no carrier frequency) fromthe received ASK signal and also detects noise. A pulse detecting part23 checks a signal from the signal receiving part 21 by a predeterminedunit for compensating errors in the signal detecting part 22. A signaldetermining part 24 determines and restores a signal to be restoredaccording to output signals from the signal detecting part 22 and thepulse detecting part 23.

The signal receiving part 21 has a pre-amplifying part 21a and aquantizing (or digitizing) part 21b. After amplifying the amplitudeshift keyed input signal to a predetermined amplitude in thepre-amplifying part 21a, the signal receiving part 21 digitizes theamplified signal in the quantizing part 21b. The signal receiving part21 produces a signal having an amplitude shift keyed carrier frequencycorresponding to a binary digit. On the other hand, the signal receivingpart 21 outputs a signal without a carrier frequency (low bit data) forthe remaining binary digits.

The signal detecting part 22 includes an oscillating part 22a, an ASKedge counting part 22b, and a comparing part 22c. The oscillating part22a generates a clock signal for a predetermined cycle (for example, acounting cycle of 13 μs) informing the ASK edge counting part 22b tostart counting. For example, the oscillating part 22a generates a 1 μspulse during a 13 μs cycle. That is, pulses having `0` during 12 μs andhaving `1` during 1 μs are generated. The pulses are generated by, forexample, 13 counters receiving a 1 MHZ clock signal. The ASK edgecounting part 22b counts up the edges of the amplitude shift keyed andreceived signal according to the clock signal for a predetermined cyclereceived from the oscillating part 22a. The clock signal of apredetermined cycle informing the ASK edge counting part 22b to startcounting generated in the oscillating part 22a is produced atpredetermined intervals irrespective of bit time.

Accordingly, the ASK edge counting part 22b determines a presence of thecarrier frequency every 13 μs, for example. In other words, the ASK edgecounting part 22b counts a pulse edge for 12 μs during the 13 μs cycle.The ASK edge counting part 22b is cleared during the remaining 1 μs, andthe counted value is applied to the comparing part 22c. The comparingpart 22c compares the counted value from the ASK edge counting part 22bwith a predetermined reference value. As an example, for a received ASKcarrier frequency of 500 KHz, the comparing part 22c uses apredetermined reference value of 6. For example, if data in a highsection of the pulse in the quantized signal is "1" and the othersection is "0", the ASK counting part 22c counts a number of pulse edgesin the high section.

In an IR(Infrared) communication, in general, a signal oscillation of500 KHz is made for data of "1" and a low bit data is outputted for dataof "0". For data of "1," a count is performed 6 times during 13 μs. Forexample, when a transmission rate is as low as 2400 bps, a cycle of onebit time is 417 μs. Since the signal has a frequency of 500 KHz,approximately 208 pulses are present in one bit time. The comparing part22c determines within ±20% error whether the signal has a carrier signalby comparing a received counted value to a reference value. Thecomparing part 22c determines that the signal has a carrier signal ifthe counted value from the ASK edge counting part 22b falls in a rangeof "4" to "8" which is a value after considering the ±20k error on 6pulses. If the counted value is not within the range, the comparing part22c determines that the signal has no carrier signal.

The pulse detecting part 23 generates a signal for compensating errorsof the signal detecting part 22 and includes a counter and a controllogic. As explained above, for the normal ASK signal without any noise,the signal oscillates with a frequency of 500 KHz for "1" data. However,even for cases where it is certain that the data is "1," if the signalhas a weak noise in any of the section oscillating with the 500 KHzfrequency, a pulse width oscillating with the 500 KHz in a portionhaving the noise becomes longer. If this happens, the counted value ofthe pulse edge portions in predetermined intervals in the ASK edgecounting part 22b does not satisfy the predetermined range of 4 to 8.Accordingly, even though it is "1" data, the "1" data is not detected as"1" data. However, the pulse detecting part 23 compensate for such anerror. Then, the signal determining part 24 receives output signals fromthe comparing part 22c and the pulse detecting part 23.

The signal determining part 24 includes a counter and random part 24aand a hexadecimal counting part 24b. The counter and random part 24a anda hexadecimal counting part 24b receive the outputs from the pulsedetecting part 23 and the comparing part 22c and remove the possibilityof signal distortion from noises. Specifically, the counter and randompart 24a combines the signals from the ASK edge counting part and thepulse detecting part to restore a signal. In addition, the counter andrandom part 24a transmits a binary digit corresponding to one bit timeto the hexadecimal counting part 24 at a transmission rate (for example,2400, 4800, or 9600 bps) using a clock signal having a speed 16 timesthe signal transmission rate.

The operation of the ASK receiver in accordance with a preferredembodiment of the present invention will now be explained.

Referring to FIG. 3, an amplitude shift keyed signal received externallyfrom the ASK receiver is amplified to a predetermined amplitude in thepre-amplification part 21a and quantized in the quantizing part 21b. Thequantized signal includes a signal having an ASK carrier frequencycorresponding to one binary digit and signals having no carrierfrequency for the remaining binary digits. The output from the signalreceiving part 21 is sent to the signal detecting part 22 including theASK edge counting part 22b and to the pulse detecting part 23. The ASKedge counting part 22b counts edge portions of signals that is outputtedfrom the signal receiving part 21 in every 13 μs intervals generated inthe oscillating part 22a. Counting the edge portions determines whetherthe transmitted signal has a carrier frequency. When a next oscillationfrequency is generated, the ASK counting part 22b is cleared, and thecounted value is transmitted to the comparing part 22c.

The comparing part 22c determines whether the signal has a carrierfrequency by comparing the counted value received from the ASK edgecounting part 22b with a reference value. In other words, the comparingpart 22c confirms that a signal has a carrier frequency if the countedvalue falls in a range of 4 to 8, for example, where the reference valueis 6. Conversely, it is determined that the signal has no carrierfrequency if the counted value is not in the range. The pulse detectingpart 23 generates a signal when a data exists in the signal outputtedfrom the signal receiving part 21. The signal generated considers thesignal from the signal receiving part 21 as a normal signal even if thesignal partly has a weak noise.

Outputs from the pulse detecting part 23 and the comparing part 22c aretransmitted to the signal determining part 24. The counter and randompart 24a in the signal determining part 24 outputs the signals in thesections where the signals outputted from the pulse detecting part 23and the comparing part 22c are identical while using a clock signalhaving a speed 16 times the signal transmission rate. The hexadecimalcounting part 24b receives a signal from the counter and random part 24aand restores the signal to the original signal.

FIGS. 4A-4F illustrate signal timings in the amplitude shift keyedreceiver of the present invention.

FIG. 4A represents a signal from the signal receiving part 21 whichoscillates with 500 KHz frequency if the signal data is "1" andmaintains a low signal if the signal data is "0". FIG. 4B represents asignal from the oscillating part 22a having pulse duration of 13 μs, forexample. These pulses act as a clock signal to count oscillating pulseedge portions in the output signal from the signal receiving part 21.FIG. 4C represents a pulse waveform from the comparing part 22c showinga result of the counted oscillating pulse edge portion of an outputsignal from the signal receiving part 21 executed by the ASK edgecounting part 22b under the control of the oscillating part 22a. Thatis, if the result of edge portion counting of the pulses for 13 μs fallsin the range of 4 to 8, where the reference value is 6, the pulsechanges to a low level.

FIG. 4D represents a waveform from the pulse detecting part 23. Thesignal is changed to a low level when the outputted signal from thesignal receiving part 21 starts to oscillate. In this process, thesignal shown in FIG. 4D should be changed to a high level again if thesignal from the signal receiving part 21 does not oscillate. The signalis maintained as the low level for a predetermined period of time tocompensate for the possible error which can occur when the oscillatingpulses of the signal from the signal receiving part 21 contain weaknoises.

FIG. 4E represents a waveform from the counter and random part 24a. Thesignal is a waveform selectively taken from portions of the waveformsfrom the comparing part 22c (FIG. 4C) and the pulse detecting part 23(FIG. 4D) that satisfies the two waveforms simultaneously. The waveformfrom the counter and random part 24a is restored into an original signalfor one bit time, as shown in FIG. 4F, by the hexadecimal counting part24b.

Accordingly, the ASK receiver of the present invention has the followingadvantages. First, the ASK receiver using a digital circuit improves itsreliability. Second, integration of the receiver with other digitalcircuits is easy. Third, an ASK receiver having a lower noise can bedesigned using a low power consumption source.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the amplitude shift keyedreceiver of the present invention without departing from the spirit orscope of the invention. Thus, it is intended that the present inventioncover the modifications and variations of this invention provided theycome within the scope of the appended claims and their equivalents.

What is claimed is:
 1. An amplitude shift keyed receiver comprising:asignal receiving part receiving an amplitude shift keyed (ASK) signal; asignal detecting part coupled to the signal receiving part and detectinga signal having a carrier frequency and a noise; a pulse detecting partcoupled to the signal receiving part and checking the signal from thesignal receiving part for compensating errors in the signal detectingpart; and a signal determining part coupled to the signal detecting partand the pulse detecting part, the signal determining part determiningand restoring a signal to be restored according to output signals fromthe signal detecting part and the pulse detecting part.
 2. The amplitudeshift keyed receiver according to claim 1, wherein the signal receivingpart includes a pre-amplifying part coupled to a quantizing part.
 3. Theamplitude shift keyed receiver according to claim 2, wherein thequantizing part amplifies a signal from the pre-amplifying part anddigitizes the signal.
 4. The amplified shift keyed receiver according toclaim 1, wherein the signal detecting part includes:an ASK edge countingpart coupled to the signal receiving part; an oscillating part coupledto the ASK edge counting part; and a comparing part coupled to the ASKedge counting part.
 5. The amplitude shift keyed receiver according toclaim 4, wherein the oscillating part generates a clock signal atpredetermined intervals and triggers the ASK edge counting part to startcounting.
 6. The amplitude shift keyed receiver according to claim 4,wherein the ASK edge counting part determines a presence of carrierfrequency in a signal from the signal receiving part at predeterminedintervals.
 7. The amplitude shift keyed receiver according to claim 4,wherein the ASK edge counting part has a tolerance of ±20% error for aninput signal.
 8. The amplitude shift keyed receiver according to claim4, wherein the ASK edge counting part has a constant counting intervalrespective of a bit time.
 9. The amplitude shift keyed receiveraccording to claim 4, wherein the comparing part compares an output fromthe ASK edge counting part to a reference value.
 10. The amplitude shiftkeyed receiver according to claim 9, wherein the predetermined referencevalue includes a range of 4 to
 8. 11. The amplitude shift keyed receiveraccording to claim 1, wherein the signal determining part includes:acounter and random part receiving a clock signal and signals from thesignal detecting part and the pulse detecting part; and a hexadecimalcounting part receiving the clock signal and an output signal form thecounter and random part.
 12. The amplitude shift keyed receiveraccording to claim 11, wherein the counter and random part combinessignals from an ASK edge counting part and the pulse detecting part torestore a signal.
 13. The amplitude shift keyed receiver according toclaim 12, wherein the counter and random part transmits a binary digitcorresponding to one bit time to the hexadecimal counting part at atransmission rate using a clock signal having a speed 16 times thetransmission rate.
 14. The amplitude shift keyed receiver according toclaim 1, wherein the signal receiving part outputs a signal having anamplitude shift keyed carrier frequency corresponding to a binary digitand a signal without the carrier frequency for the remaining binarydigits.
 15. An amplitude shift keyed receiver comprising:apre-amplifying part amplifying a received amplitude shift keyed (ASK)signal to a predetermined amplitude; a quantizing part coupled to thepre-amplifying part and amplifying an output signal from thepre-amplifying part and digitizing the output signal to produce aquantized signal; an ASK edge counting part coupled to the quantizingpart and determining a presence of carrier frequency in the quantizedsignal from the quantizing part; an oscillating part coupled to the ASKedge counting part and generating a clock signal at predeterminedintervals and triggering the ASK edge counting part to start countingedges of the amplitude shift keyed signal; a comparing part coupled tothe ASK edge counting part and comparing an output from the ASK edgecounting part to a reference value; a pulse detecting part coupled tothe quantizing part and checking the output signal from the quantizingpart for compensating errors in the oscillating part, the ASK edgecounting part, and the comparing part; a counter and random partreceiving a clock signal and coupled to the comparing part and the pulsedetecting part and, counting and random part combining signals from theASK edge counting part and the pulse detecting part to restore a signal;and a hexadecimal counting part coupled to the counter and random partand receiving an output signal from the counter and random part and theclock signal and restoring the received ASK signal to a correspondingoriginal signal.
 16. The amplitude shift keyed receiver according toclaim 15, wherein the ASK edge counting part has a tolerance of ±20%error for an input signal.
 17. The amplitude shift keyed receiveraccording to claim 15, wherein the ASK edge counting part has a constantcounting interval irrespective of a bit time.
 18. The amplitude shiftkeyed receiver according to claim 15, wherein the ASK edge counter andrandom part combines signals from the ASK edge counting part and thepulse detecting part to restore the received ASK signal.
 19. Theamplitude shift keyed receiver according to claim 15, wherein thereference value includes a range of 4 to
 8. 20. The amplitude shiftkeyed receiver according to claim 15, wherein the counter and randompart transmits a binary digit corresponding to one bit time to thehexadecimal counting part at a transmission rate using the clock signal,the clock signal having a speed 16 times the transmission rate.
 21. Anamplitude shift keyed receiver comprising:a signal receiving unitreceiving an amplitude shift keyed (ASK) signal, the signal receivingpart including; a pre-amplifying part amplifying the received ASK signalto a predetermined amplified, and a quantizing part coupled to thepre-amplifying part and amplifying an output signal from thepre-amplifying part and digitizing the output signal to produce aquantized signal, a signal detecting unit coupled to the signalreceiving unit and detecting a signal having a carrier frequency and anoise, the signal detecting unit including; an ASK edge counting partcoupled to the quantizing part and determining a presence of carrierfrequency in the quantized signal from the quantizing part, anoscillating part coupled to the ASK edge counting part and generating aclock signal at predetermined intervals and triggering the ASK edgecounting part to start counting edges of the amplitude shift keyedsignal, and a comparing part coupled to the ASK edge counting part andcomparing an output from the ASK edge counting part to a referencevalue, a pulse detecting unit coupled to the signal receiving part andchecking the signal from the signal receiving part for compensatingerrors in the signal detecting part; and a signal determining unitcoupled to the signal detecting unit and the pulse detecting unit, thesignal determining unit determining and restoring a signal to berestored according to output signals from the signal detecting unit andthe pulse detecting unit, including, a counter and random part receivinga clock signal and coupled to the comparing part and the pulse detectingpart and, the counting and random part combining signals from the ASKedge counting part and the pulse detecting part to restore a signal, anda hexadecimal counting part coupled to the counter and random part andreceiving an output signal from the counter and random part and theclock signal and restoring the received ASK signal to a correspondingoriginal signal.